737 Fuel Gauge Err Codes

[LEM]

Somebody has insinuated I'm being too pedantic to require the airplane to be dispatched officially on the techlog for ERR CODES which, under the maintenance action section of the DDPG, are considered "normal".

Quote:
"The Digital Sunburst Fuel Quantity Indicators are considered to be operating normally with ERR Codes 1, 3, 5, and 7 displayed on the Simmonds indicators....."

I believe the mechanism is always the same, pilot reports a defect, engineers answer in the techlog.

And we are not supposed to bother with the MAINTENANCE (M) section of the DDPG (although of course we give it a look).

I'm sure asking is superfluous, but would anyone bother to confirm my thoughts?

Thanks.

[Fargoo]

Although i'm not familiar with these guages I get the drift of what you're saying.
As an engineer i'd say report anything that your not happy with and we'll take a look at it.
Even of the answer to your tech log entry confirms what the book says at least you've done your bit.
I'd have thought an error code was pointing to something that needs looking at ?

Airbus would put this down as a Class 3 fault - fine for now, will be looked at under scheduled maintenance. No log book entry required.

[spannersatcx]

We have a similar scenario on our 747-200 freighters. If an error code is displayed on a qty ind then the crew WILL write it in the tech log and we WILL action it.

Now in the M(aintenance) part of the MEL it says
"With digital fuel quantity gauges installed, ERR and an error code may be displayed when the indicator test switch is pressed.
When ERR and error code 1, 3 or 6 are displayed, the fuel quantity indicator reading will be normal and the gauge is considered to be operating normally.
With other codes displayed, the gauge reading will be zero or blank and it must be considered inoperative."

Although the codes may be different as is the system, what this means to me is that I will either fix the fault or if I can't do that then I will raise an ADD. This is where the crux of the matter is, if you read what it says - there is an error but it does not affect the indicator reading - what that means is I don't have to carry out the rest of the maintenance procedure which is to then carry out fuelling by drip sticks.

So the upshot is, yes there is a fault, yes you should write it up, yes it should be fixed or MEL'd, and if it is an error code that does affect the indicator reading THEN stick checks are required.

Clear as mud me thinks!!:ok:

Just a quick edit, I don't know off the top of my head what the actual codes mean, however we do have a Manual Bulletin at work that does give the codes and what they mean, when next at work I will have a look if you like, but they are for 747!

[LEM]

Thanks for the replies; just to be more clear, my scenario is for an ERR code displayed steadily, not while doing the test.

Other Captains please?

[spannersatcx]

What we get is err on the indicator and it still reads the fuel qty. What happens when we press test is that it goes through a bite and displays all err codes, so almost the same but different.

The essence is that if the error code displayed does not effect the qty indication then no stick checks are reqd by engineering or fuel calculations by burn off by the crew. The indication is unaffected, however as said as there is an error code then an entry should be made and dealt with appropriately.

747 error codes 1, 3 and 6 are considered soft failures that do no affect the FQI. Error codes 2, 4, 5, 7, 8, 9 and 10 are hard faults that will have some form of degradation on the FQI, sometimes it will be blank read 0 or some other erroneous reading, therefore the FQI is unreliable and needs maintenance and creq action.

So with the 737 error codes of 1, 3, 5 and 7 it is a similar scenarion, yes there is an error in the system but it does not affect the qty indication and you can still use the FQI as a reliable source of actual fuel qty. Other codes 2, 4, 6 8 etc do and require action. In either case you should write the snag up and it should be actioned by maintenance either by downgrading the system where stick checks and fuel burn are monitored or in the case of the soft errors you can rely on the FQI as being accurate and no further action is required until fixed within the time scale as dictated by the MEL, say 10 days.

Hope that helps.:ok:

[LEM]

Thanks spannersatcx,
no doubt there are no real concerns about operating the airplane, my doubt is just about the legal aspect of dispatching with an ERR displayed, even if the qty is still reliable.

[nomorecatering]

Spanners at cx.

Once again you prove to be a goldmine of information, particularly in the way you can explain technical issues in a way that non engineers can unerstand. Exactly what PPRuNe is all about.

Well done sir as allways, ur a true legend of PPRuNe!

[spannersatcx]

Your welcome, thanks for the kind words :O nice to be appreciated, now all I have to do is convince my boss.....................!

LEM if it's stated in the MEL then you have to take it to be legal.

[CaptainSandL]

From the website (http://www.b737.org.uk/fuel.htm) ...

Digital Fuel Quantity Indicator Error Codes

Error Code
Fuel Quantity Indicator Reading
Probable Cause

0 Zero, Missing or disconnected tank unit
1 Normal, Tank contamination
2 Zero, Bad HI-Z lead
3 Normal, Bad compensator unit wiring
4 Zero, Bad tank unit wiring
5 Normal, Bad compensator unit
6 Zero, Bad tank unit
7 Normal, Contamination/water in compensator
8 Zero, Bad fuel quantity indicator
9 Normal, or zero Improperly calibrated indicator
. Blank, Bad fuel quantity indicator

Sorry about the loss of formatting but basically with odd error codes the gauges continue to indicate normally, but with even error codes the gauge will indicate zero.

To add to spanners excellent post, if the fault means that the gauge indicates blank, then common sense dictates that you should not go, but check the fine print in the MEL.

S & L

[LEM]

Hi Chris,
I was hoping to hear from you.

But... may I dare to insist on my specific question?

If at the gate you have a steady ERR code 3 (3 as an example), what do you do?

Do you require the aircraft to be dispatched with an entry in the techlog, or do you just ignore the problem and depart without such any entry?

This is my question: the legal aspect of departing without any entry in the techlog for an ERR code which, in fact, is "normal" according to the MAINTENANCE section of the MEL, but which you are NOT supposed to deal with.



One little suggestion to improve your wonderful website, Chris, if I might:

the Fuel Quantity Indicators you have depicted for the - 3/4/500's are the Smiths ones.

According to the DDPG, for this kind of gauges the acceptable codes are only 1, 3 and 6.

The other bunch of acceptable codes, (1,3,5,7) are for the other type of gauges, the Simmonds ones, (not depicted on your site... btw if you wish I can send you a picture in a few days, as we have a fleet completely mixed up with all sort of classics coming from every f****** corner of the world).

The Smiths ones have a less detailed ring scale, 5% "big" squares, while the Simmonds have 2% smaller squares.

Looking forward for your thoughts about my question.

LEM

[CaptainSandL]

Hi LEM,

Strictly speaking if you have any defect it must go in the tech log.

What next? Ideally you will call an engineer and have them fix it. If they can’t or there is no engineering support at destination then you consult the MEL to see if you can bring it home. Many defects are not stoppers and those that are, you really don’t want to fly with. Most airlines have a procedure whereby you can transfer the defect yourself to the status of an Acceptable Deferred Defect (or similar terminology) and follow the steps and/or limitations in the MEL.

In practice most people will look at the MEL first before making a tech log entry to see how serious it is and then decide whether or not to: a) Call out an engineer; b) Make a tech log entry an ADD it; or c) Carry it with out writing anything until the end of the day or next crew change.

In your situation with an acceptable error code, ie gauge still indicating normally, I would probably first mention it to an engineer if there was one available; if not and I knew that the error code was OK then I would put it in the tech log at the end of the day. That way there is a formal record of the error and your maint org will be obliged to investigate. If the error code caused the gauge to blank, then the gauge is clearly u/s, make a tech log entry immediately and follow the MEL restrictions.

Legally however, you should put any observed error code in the tech log whenever you see it, in this case it would be in the cockpit preparation before departure. You must then transfer it to an ADD or have it fixed. Either way a record of the error will be left on the ground with the loadsheet etc after you have got airborne.

Hope this helps

S & L

PS Thanks for the info/suggestion. I don’t seem to fly many classics these days so would appreciate the photo.

Brgds

CB

[B737MRG]

Hi Chris,

error codes for both Simmonds and Smiths are in my book

Pat

[Golden Rivet]

AIRPLANES WITH SMITHS SUNBURST FUEL QUANTITY INDICATORS

Digital fuel quantity indicators show the weight of fuel in each fuel
tank. Each fuel quantity indicator has a single chip microcomputer
system and a digital liquid crystal display (LCD). The microcomputer
measures capacitive and resistive current in the tank units. The
microcomputer also monitors the leakage current and other circuit
parameters. When a parameter reaches an unacceptable level an error code
is shown on the indicator face. The display will show ERR plus an error
code between 0 and 10 which will be used to help in troubleshooting the
system. The subsequent define the error codes.

1 Normal Open or short in COMP LO-Z line
2 Zero Short in compensator unit (HI-Z to COMP LO-Z)
3 Normal Excessive compensator unit leakage
4 Zero Open or short in TANK LO-Z line
5 Zero Short in tank unit (HI-Z to TANK LO-Z)
6 Normal Excessive tank unit leakage
7 Calibration unit failure
8 Blank Error in DCTU data
9 Indicator memory failure
10 Zero Open or short in HI-Z line

If at the gate you have a steady ERR code 3 (3 as an example), what do you do?

If you know what the code means, use your common sense and snag it at the end of the flying day, if not, get an Engineer out to have a look.

[CaptainSandL]

Hi ASFKAP,

I follow your logic, but I could never advocate a pilot clearing the fault himself, especially by pulling c/b’s, without making a tech log entry. This will enable the maint company to spot any trends in reoccurring faults, spurious or otherwise.

Let me give you a hypothetical example of how a pilot and an engineer would view the same problem. Say a test shows Simmonds 7 - the error code for water contamination (I only use this example because it is an untechnical one for us pilots to understand). The crew call an engineer who clears the fault in the way you described and says “don’t worry boys the fault has cleared, it must have been spurious”. I would feel pretty uncomfortable that the engineer had only removed the indication and not the cause. Something must have caused the code to appear in the first place and I would not want to trust my life to a hunch that it was a spurious indication.

In fact, if this did happen to me, I would be asking for a water check in the tank which had showed the error code. I would guess that any pilot who had ever found water in the tanks of his Cessna 150 all those years ago would do the same.

S&L

[B737MRG]

Hi Chris,

I fully agree with your viewpoint.

I always get angry when I read maintenance reply "checked on ground and found OK" as if pilots have reported a problem that never existed. It happened to me (again) this week when I wrote something in the Tech Log and departed with the same aircraft next day. I called maintenance to SHOW them the problem was still present. (for info ; the Landing Light remained ON when placing the switch gently to OFF - I had flown with the Light ON during 2 hours of flight)

Now referring to those Error Codes, as I said, I agree. But on the other hand, you would depart with water in your Fuel Tank on NG as it hasn't got any error code "7" displayed to the crew ?

Pat